Digitalis is of benefit to some patients with heart failure who have normal sinus rhythm, but not to all; how to select those who will benefit has not been established. The work proposed here is a prospective, randomized, double-blind crossover trial of digoxin vs. placebo (nine weeks of each) in adult outpatients with heart failure accompanied by sinus rhythm (and unassociated with valvular heart disease) that is due to one of four clinical syndromes: cardiomyopathy syndrome due to coronary artery disease; idiopathic congestive cardiomyopathy; heart failure associated with hypertension; and unexplained heart failure of the elderly. Whether the degree of heart failure worsens during the placebo period will be measured by a combination of signs, symptoms, chest film data, weight, pulmonary function tests, and diuretic requirement. Left ventricular ejection fraction will be measured by multigated cardiac blood pool scan. Data will be examined with regard to whether clinical benefit from digoxin is predictable by baseline left ventricular ejection fraction, digoxin-induced change in left ventricular ejection fraction or change in systolic time intervals, left ventricular wall thickness (echocardiographic), clinical syndrome, or by a combination of these. The study population is representative of the majority of patients with heart failure in the United States. In view of the substantial incidence of digitalis intoxication among patients taking digitalis, it is important that the degree to which digitalis is efficacious for patients in the study population or in its subsets be established. In patients who demonstrate a reproducible clinical response to digitalis, the minimum effective dose producing the response will be determined.